Combined Cycle Power Plants. Combined Cycle Power Plant Overview (Single- and Multi-Shaft) Training Module. ALSTOM (Switzerland) Ltd )*+,

Transcription

1 Power Plant Overview Training Module ALSTOM (Switzerland) Ltd )*+,

2 We reserve all rights in this document and in the information contained therein. Reproduction, use or disclosure to third parties without express authority is strictly forbidden. Copyright by ALSTOM (Switzerland) Ltd 2004 This is a training module. All mentioned / attached values and settings are for information only. The values might be changed during commissioning. For actual values please refer to the Instruction Manual. CSXA220021enC Page 2

3 Table of Contents List of Technical Aids... 4 Module Objectives... 5 Overview... 6 Gas Turbine Power Plant Overview... 6 Gas Turbine Main Components and Functional Principle... 7 Generator Components and Functional Principle... 8 Steam Turbine Power Plant Overview Basic Components of a Steam Turbine Power Plant Power Plant Overview Multi-Shaft Arrangement Single-Shaft Arrangement Overview of a Plant for CHE Supply Multi-Shaft Arrangement Overview of a Plant for CHE Supply Single-Shaft Arrangement Control and Protection System Overview Summary Figure 1: Simplified Overview of a Gas Turbine Power Plant, its Major Components and Systems Figure 2: Simplified Overview of Steam Turbine Power Plant, its Major Components and Systems Figure 3.1: Power Plant Process Overview (Multi- Shaft) Figure 3.2: Power Plant Process Overview (Single- Shaft) Figure 3.3: Plant for CHE Supply and Multi-Shaft Arrangement Figure 3.4: Plant for CHE Supply and Single-Shaft Arrangement Figure 3.5: CHE Supply Plant Figure 4: Basic Scheme of the Control of a Power Plant Figure 5: Simplified Water Steam Cycle CSXA220021enC Page 3

4 List of Technical Aids Definitions Enclosure Integral Standard Document Attachment Attached Site-Specific Illustration or Document Identification Attachment 1 Description Plant Operation and Control Concept CSXA220021enC Page 4

5 Module Objectives Upon completion of this section, the trainee is able to: State why combined cycle power plants are used in preference for supplying electric energy. Explain why a gas turbine set includes: A turbine A combustion chamber A compressor Give the reasons why the main electrical energy supply chain contains: A generator An exciter Generator bushings A generator breaker A main step-up transformer A grid breaker Justify the use of a boiler and a steam turbine within a steam turbine power plant. Explain the reasons why the following components are used within a combined cycle power plant: Heat recovery steam boiler Condenser Deaerator and feed water storage tank Justify the use of a combined cycle plant as a process for combined heat and electricity (CHE) supply. State the reasons why a combined cycle power plant includes in its automation system the following components: Gas turbine electronic controller (EGATROL) Steam turbine electronic controller (TURBOTROL) Steam Turbine generator set sequencer (TURBOMAT) Voltage regulator (UNITROL) Synchronizer (SYNCHROTACT) Generator protection (GSX or REG) Heat recovery steam boiler controller (BOILERMAT) CSXA220021enC Page 5

6 Overview CCPP as energy supplier A relative newcomer to the field of energy supply is the combined cycle power plant (CCPP). CCPPs take the advantages of gas turbosets and steam turbosets and combine them in a system that provides electric power at a much higher efficiency than is possible with either system operating alone. This section will briefly describe the process of typical ALSTOM gas and steam turbine power plants before summarizing how those processes are combined in a typical CCPP. The material does not describe all equipment, but rather focuses on major components, which are essential to an understanding of the overall process. Gas Turbine Power Plant Overview Basic components of a gas turbine power plant Refer to Figure 1. ALSTOM produces a variety of gas turbosets which differ in: configuration and electric power output. However, the basic energy conversion process from chemical energy to mechanical energy to electrical energy is similar from machine to machine. The supply of electric energy from a gas turbine power plant requires the use of: a gas turbine a generator an exciter generator bushings a generator breaker a generator step-up transformer and a grid breaker. The role of each will be briefly described. CSXA220021enC Page 6

7 Gas Turbine Main Components and Functional Principle Figure 1 Gas Turbine The gas turbine is composed of three processing elements: an air compressor a combustion chamber and the turbine itself The turbine itself: Converts the thermal energy contained in the combustion gas into mechanical energy at the coupling and Is the prime mover that drives the generator and the compressor. Is driven by hot, compressed combustion gas that strikes blading mounted on the rotor, and causes it to turn. After the combustion gas passes through the turbine it is discharged to atmosphere and is called exhaust gas The combustion gas that drives the turbine is supplied by the combustion chamber. The latter one: Converts the chemical energy of the fuel into heat and Is an enclosed, pressurized firing place where air and liquid and/or gaseous fuel are continuously burned. The pressurized air required for combustion is delivered by the compressor. The latter one: Converts mechanical energy into pneumatic energy and Is driven by the turbine through a common shaft. The air within the compressor is pressurized with the help of rotating and stationary blading. Pressurized air is also used for sealing and cooling of the set. Fuel Throughput Control The fuel throughput to the combustion chamber is controlled by the appropriate setting of control valves, which can assume, hold and change to any position between fully closed and fully open. CSXA220021enC Page 7

8 Generator Components and Functional Principle Figure 1 Generator The generator: Is the driven machine and Converts the mechanical energy of the turbine into electrical energy. Is composed of A non-movable part called the stator and A movable part called the rotor. The latter is coupled to the turbine rotor, either; directly or through a rotational speed reduction gear The rotor: Is basically a magnet and Creates a rotating magnetic field inside the machine by means of the excitation or field winding, often referred to simply as the rotor winding. The strength of the magnetic field must be adjusted to correspond to the electrical power output of the generator. The consequences of this measurement are: The generator is kept in synchronism with the grid and Both generator voltage and the reactive power supplied to the grid are kept within specified limits. This is accomplished by means of a direct current: Referred to as an excitation current and Passed through the rotor field winding. The automatic voltage regulator (AVR) equipment controls the excitation current in turn. The latter one controls both: The terminal voltage of the generator and The reactive electric power supply to the grid. The stator contains fixed windings inside which an alternating voltage is induced by the rotating magnetic field. (Continued next page) CSXA220021enC Page 8

9 Generator Components and Functional Principle (continued) Figure 1 Exciter The exciter provides the direct current (DC) for the windings of the generator s rotating magnetic field. Two types of exciters are used: brushless and static Both perform the same function. Generator Bushings The generator s bushings: Provide the connection that enables the electric energy of the generator to be delivered to the outside world. Are mounted on the generator stator housing and Receive the high voltage (HV) output of the stator windings. The Generator Breaker The generator breaker provides the electrical connection between the generator s bushings and the step-up transformer. Main Step-up Transformer The main step-up transformer: Is used to match the outlet voltage of the generator to the voltage of the grid or network. Also works like an electric buffer in case of short circuit in the grid, protecting the generator Grid Breaker The grid breaker: Provides the electrical connection between the substation and the grid or network. Disconnects the gas turboset from the grid in case of network failures, allowing it to run on island duty. Is an optional piece of equipment. CSXA220021enC Page 9

10 Steam Turbine Power Plant Overview Basic Components of a Steam Turbine Power Plant Figure 2 The supply of electricity from a steam power plant requires: a water steam cycle with: a boiler a steam turbine a generator an exciter generator bushings circuit breaker and step-up transformer. The role of each will be briefly described. Boiler The boiler: Is a place where an energy conversion takes place, namely from chemical energy of the fuel into heat energy. The latter one is carried by the combustion gas. Uses heat of combustion to convert water into steam, a physical conversion process. To secure the integrity of the boiler, it must be fed continuously with water. Figure 2 High pressure (HP) steam lines forward the steam raised in the boiler to the steam turbine. The steam massflow, which passes through the turbine, is regulated by the opening of control valves. As steam flows through the turbine it strikes blades on the rotor, causing them to turn. This is an energy conversion process from heat energy to mechanical energy. The conversion from mechanical to electrical energy then takes place through the generator and exciter in a process, which is essentially the same as that described above for the gas turboset. CSXA220021enC Page 10

11 Power Plant Overview Multi-Shaft Arrangement Figure 3.1 The objective of a combined cycle power plant with multi-shaft arrangement is to deliver only electricity. To fulfil the above objective, the major components of a multiple shaft combined cycle power plant are: One or more gas turbosets. One or more heat recovery steam boilers (HRSB). One or more steam turbosets. The rest of the water-steam cycle. The balance of plant equipment: mechanically and electrically. Control equipment. The process begins when the gas turboset is placed in operation. The gas turbine operates on a mixture of air and fuel, which is ignited in the combustion chamber. The hot gas is expanded through the turbine, causing the shaft to rotate. The turbine-compressor rotor is connected to the generator rotor: Either directly or Through a rotational speed reduction gear. The generator converts the mechanical energy into electrical energy, which it supplies to the grid or network. Exhaust gasses from the combustion process leave the vas turbine at a very high temperature. If the gas turbine is operated in single cycle, this heat energy is: Discharged to atmosphere and Thus wasted. However, if the gas turbine is operated in combined cycle, the hot gas flow is directed to an HRSB. Here, the heat from the hot gas converts water in the HRSB into steam. That is, the HRSB links together the gas turbine process and the water steam cycle. When the steam is at the correct temperature and pressure, it is forwarded to the steam turbine where it expands through the turbine. Its mechanical power is transmitted via the shaft to the generator, which provides additional electric power for the grid. (Continued next page) CSXA220021enC Page 11

12 Multi-Shaft Arrangement (continued) Exhausted steam is directed to a condenser, where it is converted to water called condensate. The condensate is then directed to the feed water storage tank-deaerator. Here it is: Deaerated Preheated and Stored The feed water is then used by the HRSB in the throughput demanded by gas turbineset electric power output. Single-Shaft Arrangement Figure 3.2 The objective of a combined cycle power plant with single-shaft arrangement is to deliver only electricity. To fulfil the above objective, he major components of a single shaft combined cycle power plant are: A gas turbine. An alternator. A self shifting and synchronizing (SSS) clutch. A water steam cycle, mainly composed of: A heat recovery steam boiler. A steam turbine alternator set. A condenser. Condensate extraction pumps. A deaerator feedwater storage tank. Boiler feedwater pumps. Mechanical balance of plant equipment. Electrical balance of plant equipment. Control equipment. The single shaft combined cycle power plant functions in the same way as the multiple shaft arrangement. The most important difference is the application of the SSS clutch. The latter one permits the ST: To be accelerated AND To be connected to the alternator, already being driven by the GT The SSS clutch: Engages automatically as soon as the torque from the ST shaft becomes positive; that is: As soon as the rotational speed of the ST tends to overtable that of the alternator Disengages automatically as soon as the torque of the ST shaft becomes negative CSXA220021enC Page 12

13 Overview of a Plant for CHE Supply Multi-Shaft Arrangement Figure 3.3 The objective of a combined cycle plant for CHE supply with multi-shaft arrangement is to deliver simultaneously heat and electricity. This process is known as combined heat and electricity (CHE) supply. To fulfil the above objective, the major components of a multiple shaft combined cycle plant for CHE supply are: One or more gas turbosets. One or more heat recovery steam boilers (HRSB). One or more steam turbosets. One or more heating condensers. The rest of the water-steam cycle. The balance of plant equipment: mechanically and electrically. All the previous descriptions apply to this type of combined cycle plant plus the following explanations: The heat supply happens normally with one of the two heat carriers: steam or water. Steam is normally extracted at some stage of the steam turbine. This steam can then be used directly for heating purposes or this steam can be used indirectly for heating purposes across a corresponding heat exchanger. Depending on heat demand, the supply of this energy form can be completely suspended. In this case the combined cycle plant runs only delivering electricity. Figure 3.5 An interesting alternative is the arrangement of a combined cycle plant for CHE supply, but without the steam turbine alternator set in the water steam cycle. The heat from the HRSB is used in this case directly for industrial processes like: petrochemical plants, sea water desalination plants, district heating, etc. Normally in this case, the HRSB is equipped with supplementary inlet duct burners to secure the heat supply if the gas turbine alternator set is out of duty. CSXA220021enC Page 13

14 Overview of a Plant for CHE Supply Single-Shaft Arrangement Figure 3.4 The objective of a combined cycle plant for CHE supply with single-shaft arrangement is to deliver simultaneously heat and electricty. This process is known as combined heat and electricity (CHE) supply. To fulfill the above objective, the major components of a single shaft combined cycle plant for CHE supply are: A gas turbine. An alternator. A self shifting and synchronizing (SSS) clutch. A water steam cycle, mainly composed of: A heat recovery steam boiler. A steam turbine alternator set. A condenser. A heating condenser. Condensate extraction pumps. A deaerator feedwater storage tank. Boiler feedwater pumps. Mechanical balance of plant equipment. Electrical balance of plant equipment. Control equipment. All the previous descriptions apply to this type of combined cycle plant plus the following explanations: The heat supply happens normally with one of the two heat carriers: steam or water. Steam is normally extracted at some stage of the steam turbine. This steam can then be used directly for heating purposes or this steam can be used indirectly for heating purposes across a corresponding heat exchanger. Depending on heat demand, the supply of this energy form can be completely suspended. In this case the combined cycle plant runs only delivering electricity. CSXA220021enC Page 14

15 Control and Protection System Overview Importance of automated control systems Today's complex power plants operate at very high efficiency because of the sophisticated design of the equipment used. To reach these high levels of efficiency and reliability, automation systems have become standard in the industry. ALSTOM's major control and protection systems are briefly outlined below. Details are provided in the respective gas and steam turbine modules. Figures 1 and 4 EGATROL EGATROL: Is the abbreviation for electronic gas turbine controller. Includes a sequencing program that automatically starts, loads and shuts down the gas turboset and its auxiliaries while observing ALSTOM protective limitations. Regulates during operation, the gas turboset by positioning the fuel control valves based on electric power output requirements. Includes a man machine interface (MMI): For receiving data from the process. To influence the process. Activates the safety system. The latter one, when it is actuated, protects the gas turboset from damage by tripping the fuel stop and control valves to their closed positions. This immediately: stops the fuel throughput to the combustion chambers interrupts the combustion process and shuts down the turboset Figures 2 and 4 TURBOTROL TURBOTROL: Is the steam turbine controller. Provides control and regulation of the steam turbines. Performs its function by positioning the steam control valves. The latter ones regulate the steam throughput across the turbine, based on system requirements. Activates the safety system. The latter one, when it is actuated, protects the steam turboset from damage by tripping the steam stop and control valves to their closed positions. This immediately stops the flow of steam to the turbine. (Continued next page) CSXA220021enC Page 15

16 Control and Protection System Overview (continued) Figures 2 and 4 TURBOMAT The TURBOMAT: Is the steam turboset sequencer. Is optional equipment. When supplied is used to automatically start-up, load, and shut-down the steam turboset and its auxiliaries while observing ALSTOM limitations. Figures 1 and 2 UNITROL The UNITROL: Is the excitation system for the alternators. Includes a centerpiece that is the automatic voltage regulator (AVR). The latter one: Maintains the outlet voltage of the generator at a constant value. Influences the exciter and thereby the electric current through the windings of the magnetic field. Has a back-up manual field current regulator (FCR). The latter one: Fulfills the same task but requires manual input from the operator. Adjusts the reactive electric power output of the generator, expressed in units of voltampere reactive (V A r ). Figures 1 and 2 SYNCHROTACT The SYNCHROTACT: Is the synchronizer of the turbosets. Can be operated automatically or manually. Interacts with: Gas and steam turbine controllers and UNITROL Matches the following parameters of the generators and the grid: outlet voltage frequency and phase sequence When synchronization is completed, the generator breaker closes. (Continued next page) CSXA220021enC Page 16

17 Control and Protection System Overview (continued) Figures 1 and 2 GSX or REG: The generator protection system: Protects the generator and its associated equipment from abnormal operating conditions. When the protection equipment detects a fault: The generator breaker is opened and The gas or steam control valves are tripped to their closed positions. Has the designation GSX or REG, depending the selected model. Figure 4 BOILERMAT Each HRSG has several function groups and drives. The BOILERMAT: Is the boiler controller. Coordinates different control functions of the HRSB like: start-up shut-down and open-loop controls This coordination is made in respect with the open-loop controls of the gas and steam turbosets. Regulates during operation, the HRSB's drum level closed-loop controls. Figure 4 Miscellaneous Controller The miscellaneous controller takes care of the different components of the water steam cycle like: the condenser the condensate extraction pumps the deaerator the boiler feed water pumps Figure 4 BOP Equipment Controller BOP is the abbreviation for balance of plant. Practically each BOP equipment has its own controller. To indicate that their functions must be coordinated, the concept of the BOP equipment controller is introduced. Figure 4 lists the most common BOP equipment s of a typical combined cycle power plant. (Continued next page) CSXA220021enC Page 17

18 Control and Protection System Overview (continued) Figure 4 BLOCKMASTER The BLOCKMASTER: Is the overimposed power plant controller. Ensures that each major component in the CCPP process is brought into service or removed from service in the proper sequence. Is also called UNITMASTER. Includes several MMIs: For receiving data from the process. To influence the process. Summary This section: Described the components used to deliver electricity from modern gas and steam turbine power plants. Included information of how those single processes are joined to operate at higher efficiency in a combined cycle arrangement to deliver only electricity or simultaneously electricity and heat. To ensure that you understand the material covered, review each of the Objectives (page 5). CSXA220021enC Page 18

19 CSXA220021enC Page 19 Fuel Chemical Output: exhaust gas (heat) T EG Turbine fuel valves trip and control Turbine Heat Combustion chamber Gas turbine electronic controller - Sequencing - Control/ regulation - Protection ( EGATROL) * n Inputs: air fuel Rotor Compressor Gas turbine block P el f Air Mechanical n Turbine Generator protection ( GSX/ REG) Coupling P el Output: mechanical energy U G Neutral point Stator Rotor field Generator U G / f Generator block G U G Output: electric energy High voltage bushings DC Synchronizer (SYNCHROTACT)* Voltage regulator (UNITROL) * Exciter: brushless or static MV Generator breaker Electrical U N MV / f N Generator step-up transformer : Main electric energy supply : Feedback signal : Actuation signal : Information exchange signal P : Electric power n : Rotational speed T : Exhaust gas temperature f : Frequency Differential current U : Generator voltage U : Net voltage f : Generator frequency f : Net frequency MV : Medium voltage el G N G N Grid breaker Electrical energy to consumers * Trade names for ABB equipment CSXA cdr Figure 1: Simplified Overview of a Gas Turbine Power Plant, its Major Components and Systems )*+,

20 CSXA220021enC Page 20 Chemical Heat Mechanical Inputs : Water Fuel Air Exhaust gas Steam Water Boiler feedwater pump Steam turbine electronic controller - Control - Regulation - Protection ( TURBOTROL) * Turbine steam valves trip and control Boiler Main steam P S Deaerator and feed water storage tank T S n G Steam turbine Make- up water P el Condenser Rotor Condensate extraction pump Steam and water vapor Condensate ( Water) Turbine- generator set sequencer ( TURBOMAT) * f G Coupling Generator protection ( GSX/ REG) * P el Neutral point Cooling medium in Cooling medium out Generator stator Generator field f G U G U G High voltage bushings Synchronyzer ( SYNCHROTACT) * Voltage regulator ( UNITROL) * Exciter: brushless or static Electrical Generator breaker f N U N Generator step- up transformer Grid breaker * Trade names for ABB equipment : Main electrical energy supply : Feedback signal : Actuation Signal : Information exchange signal P : Electrical power n : Rotational speed of generator f : Frequency of generator U : Voltage of generator f : Frequency of net or grid U : Voltage of net or grid Differential current P : Steam pessure T : Steam temperature el G G G N N S S OUTPUT: Electrical energy to consumers CSXA CDR Figure 2: Simplified Overview of Steam Turbine Power Plant, its Major Components and Systems )*+,

21 CSXA220021enC Page 21 Low pressure economizer Natural gas Low pressure evaporator Intermediate pressure economizer Intermediate pressure evaporator High pressure economizer Intermediate pressure superheater High pressure evaporator High pressure superheater and intermediate pressure reheater Fuel gas preheater HRSB Gas turbine Heat recovery steam boiler LP IP HP steam drum steam drum steam drum Compressor Combustion chamber Feedwater control valve Low pressure water circulation pump Intermediate pressure water circulation pump High pressure water circulation pump Generator G Deaerator feedwater storage tank Low / intermediate pressure feedwater pump High pressure feedwater pump Steam pressure reducing valve HP steam turbine IP steam turbine Main condenser Low pressure deaeration steam control valve LP steam turbine G Generator Cooling Medium Condensate extraction pump CSXA cdr Figure 3.1: Power Plant Process Overview (Multi- Shaft) )*+,

22 CSXA220021enC Page 22 Low pressure economizer Natural gas Low pressure evaporator Intermediate pressure economizer Intermediate pressure evaporator High pressure economizer Intermediate pressure superheater High pressure evaporator High pressure superheater and intermediate pressure reheater Fuel gas preheater HRSB Gas turbine Heat recovery steam boiler LP IP HP steam drum steam drum steam drum Compressor Combustion chamber Feedwater control valve Low pressure water circulation pump Intermediate pressure water circulation pump High pressure water circulation pump Generator G Deaerator feedwater storage tank Low / intermediate pressure feedwater pump Self shifting and synchronicing clutch High pressure feedwater pump Steam pressure reducing valve HP steam turbine IP steam turbine Main condenser Low pressure deaeration steam control valve LP steam turbine Cooling Medium Condensate extraction pump CSXA CDR Figure 3.2: Power Plant Process Overview (Single- Shaft) )*+,

23 Figure 3.3: Plant for CHE Supply and Multi-Shaft Arrangement Air inlet Natural gas (fuel oil) Flue gases 100 C Electricity Heatrecovery steam boiler (HRSB) 500 C Generator Gas turbine Electricity Steam Steam turbine Generator Condenser Heating condenser Cooling water Feedwater District heating system CSXA CDR CSXA220021enC Page 23

24 Figure 3.4: Plant for CHE Supply and Single-Shaft Arrangement Deaerator feedwater storage tank Boiler feedwater pump Steam Steam turbine Heating condenser Circulating pump Condensate extraction pumps Condensate District heating system CSXA cdr Heat recovery steam boiler (HRSB) Air inlet Electricity SSS clutch Generator Main condenser CW circulating pump Cooling water (CW) Flue gases Natural gas (fuel oil) Gas turbine SSS: self synchronyzing and shifting CSXA220021enC Page 24

25 Figure 3.5: CHE Supply Plant Deaerator feedwater storage tank Boiler feedwater pump Heat consumer Circulating pump Condensate extraction pumps Condensate District heating system CSXA CDR Heat recovery steam boiler (HRSB) Air inlet Electricity Generator CW circulating pump Cooling water (CW) Flue gases Natural gas (fuel oil) Gas turbine SSS: self synchronyzing and shifting CHE: combined heat and electricity CSXA220021enC Page 25

26 CSXA220021enC Page 26 BOP CONTROLLER BOP equipment like: -Main cooling water -Main condenser tube cleaning system -Cooling tower -Closed cooling water system -Rain water system -Desalination plant -Water treatment plant -Waste water system -Fael gas supply system -Fuel oil supply system MMI EGATROL (open-and closedloop control) BLOCKMASTER UNITMASTER BOILERMAT (open-and closedloop control) MMI TURBOMAT (open-loop control) TURBOTROL (closed-loop control) MISCELANEOUS (water steam cycle) CSXA cdr 1 : Air compressor 2 : Combustion chamber 3 : Gas turbine 4 : Generator 5 : Exhaust gas flap or by- pass 6 : Heat recovery steam boiler 7 : Steam turbine 8 : Condenser 9 : Condensate extraction pump 10: Deaerator and feedwater storage tank 11: Boiler feedwater pump 12: Supplementary firing MMI: Man machine interface : Information exchange signal : Actuation signal : Feedback signal BOP: Balance of plant Remark: For simplicity reasons only one line is represented for: sented for: - Information exchange - Commands - Feedback informations Figure 4: Basic Scheme of the Control of a Power Plant )*+,

27 Figure 5: Simplified Water Steam Cycle Innovative cycle solution ICS: Dual pressure reheat DPR: SSPT: KA24-1 ICS / DPR / SSPT CSXA CDR Single shaft power train CSXA220021enC Page 27